Fabrication of ZnS nanoparticle chains on a protein template

RESEARCH PAPER

Fabrication of ZnS nanoparticle chains on a proteintemplate

S. Padalkar Æ J. Hulleman Æ S. M. Kim ÆT. Tumkur Æ J.-C. Rochet Æ E. Stach ÆL. Stanciu

Received: 7 November 2008 / Accepted: 23 June 2009 / Published online: 10 July 2009

� Springer Science+Business Media B.V. 2009

Abstract In the present study, we have exploited the

properties of a fibrillar protein for the template

synthesis of zinc sulfide (ZnS) nanoparticle chains.

The diameter of the ZnS nanoparticle chains was tuned

in range of *30 to *165 nm by varying the process

variables. The nanoparticle chains were characterized

by field emission scanning electron microscopy, UV–

Visible spectroscopy, transmission electron micros-

copy, electron energy loss spectroscopy, and high-

resolution transmission electron microscopy. The

effect of incubation temperature on the morphology

of the nanoparticle chains was also studied.

Keywords Nanoparticle chains � Template �Synthesis � Morphology � One-dimensional

nanostructure

Introduction

One-dimensional structures (1D) such as nanowires,

nanorods, nanoparticle chains, and nanotubes have

attracted much attention in recent years (Cui et al.

2001; Diehl et al. 2002; Huang et al. 2001; Bachtold

et al. 2001; Collins et al. 2001; Murray et al. 2000;

Kimberly et al. 2002; Johnson et al. 2002; Alivisatos

1996). Their growing importance is due to the unique

properties they exhibit. The 1D structures show future

promise in a variety of fields such as electronics,

optoelectronics, catalysis, and biosensing. Although

the advances in the field of nanotechnology are

promising, there are few obstacles that need to be

overcome. The synthesis of 1D nanostructures by

solvothermal process (Chen et al. 2003), thermal

evaporation (Meng et al. 2003; Wang et al. 2002),

liquid crystal template (Jiang et al. 2001), and

electrodeposition (Xu et al. 2006) in porous anodic

alumina templates require high temperatures or pres-

sures and the precise control of the process variables.

Moreover, after synthesis it is generally difficult to

manipulate and position the nanostructures in devices.

In turn, biological molecules have the chemical

recognition capacity that is promising in allowing

for a higher degree of flexibility in their positioning in

specific places in nanoelectronic devices. In addition,

certain peptides and proteins can self-assemble into

chemically reactive readymade shapes that can serve

as templates for further growth of inorganic nano-

structures. Biological systems possess a high degree

S. Padalkar (&) � S. M. Kim � T. Tumkur �E. Stach � L. Stanciu

School of Materials Engineering, Purdue University,

West Lafayette, IN 47906, USA

e-mail: [email protected]

S. Padalkar � S. M. Kim � E. Stach � L. Stanciu

Birck Nanotechnology Center, Purdue University,

West Lafayette, IN 47906, USA

J. Hulleman � J.-C. Rochet

Department of Medicinal Chemistry and Molecular

Pharmacology, Purdue University, West Lafayette,

IN 47906, USA

123

J Nanopart Res (2009) 11:2031–2041

DOI 10.1007/s11051-009-9689-8

of organization from molecular building blocks (pep-

tides, amino acids, proteins, and nucleic acids) and are

perfect models for bottom–up strategies for controlled

material synthesis. Their molecular recognition capa-

bilities, combined with the specificity toward certain

ions and molecules, can be used to precisely control

the fundamental processes involved in materials

synthesis and processing, such as phase stability,

nucleation and growth, pattern formation, and assem-

bly. The electroless deposition, especially on DNA

molecules and viruses, has lead to the fabrication of

several different 1D structures (Klein et al. 1997;

Keren et al. 2003; Claridge et al. 2005; Flynn et al.

2003; Yan et al. 2003; Monson and Woolley 2003;

Deng and Mao 2003; Richter et al. 2001; Dong et al.

2007; Mao et al. 2004; Huang et al. 2005; Nam et al.

2006). However, peptides and proteins, with the

ability to self-assemble into ordered fibrils have been

much less investigated. While several metallic nano-

wires, as well as CdS nanoparticle chains have been

synthesized via protein-directed nucleation and

growth in our laboratory (Padalkar et al. 2007,

2008), to our knowledge, there are no reports in

literature regarding the use of fibrillar proteins for the

template synthesis of zinc sulfide (ZnS) nanowires or

nanoparticle chains. ZnS is an II–VI semiconducting

material having a band gap of 3.7 eV. It is a

particularly interesting material due to its wide range

of potential applications. It shows promise in several

fields and has applications in electronics and photon-

ics. ZnS has semiconducting, photoluminescent, and

field emission properties. These properties have been

exploited in many applications such as light convert-

ing electrodes, ultraviolet light-emitting diodes, phos-

phors in cathode ray tubes, flat panel displays,

injection lasers, and infrared windows (Kar et al.

2003; Xu et al. 2006; Lu et al. 2007). Several ZnS 1D

structures such as nanorods, nanowires, nanobelts,

and nanotubes (Zhang et al. 2002; Yin et al. 2005; Ma

et al. 2003) have be fabricated. All these structures

have been synthesized at high temperatures and

require long reaction times. However, the fabrication

process described here was carried out at atmospheric

conditions and requires a very short synthesis time

typically not more than 15 min for the completion of

the entire experiment.

Here, we report the synthesis of ZnS nanoparticle

chains on a fibrillar protein (a-synuclein) template.

Synuclein is a 14.4 kDa amyloidogenic protein, which

is found in the human brain (Spillantini et al. 1997).

This protein has the ability to self-assemble into

fibrillar structures having an approximate diameter of

8 nm and a length between 500 nm and 1 lm

(Conway et al. 2000; Hoyer et al. 2002). The presence

of protein fibrils in the human brain can lead to

different pathologies (Serio et al. 2000; Scheibel and

Lindquist 2001; Scheibel et al. 2003; DePace and

Weissman 2002). However, when the a-synuclein

protein self-assembles into fibrils in vitro, its proper-

ties can be potentially useful for the synthesis of

inorganic nanostructures. The structure of amyloido-

genic fibrillar proteins, such as a-synuclein, is mainly

composed of adjacent b-sheets assembled into a

twisted fibrillar structure by hydrogen bonding (Vilar

et al. 2008; Serpell et al. 2000; Nelson and Eisenberg

2006; Rochet 2007). The charge on the b-sheets can

be manipulated during the self-assembly process to

obtain fibrillar structures with different charge

arrangements, thus making them ideal structural

templates for the fabrication of 1D nanostructures.

Experimental details

Self-assembly of a-synuclein fibrils

The expression and purification of a-synuclein were

carried out as previously described (Conway et al.

2000; Rochet et al. 2000). The E46K mutant of a-

synuclein, was used because it has the ability to

rapidly self-assemble into fibrils. The lyophilized

protein was dissolved in phosphate-buffered saline

(PBS) with pH 7.4, 0.02% (w/v) NaN3 and dialyzed

against the same buffer at 4 �C, for 24 h. The protein

solution was filtered through a 0.22 lm nylon spin

filter followed by a Microcon-100 spin filter, yielding

a stock solution depleted of aggregates. The final

concentration of protein in PBS was of 100–300 lM

[determined by bicinchoninic acid (BCA) assay]. The

protein was incubated at 37 �C for 12–96 h in a tissue

culture rolling drum to generate fibrils.

Synthesis of ZnS nanoparticle chains

The synthesis of ZnS nanoparticle chains was carried

out by using zinc chloride (ZnCl2; 2 mM) as the salt

solution, and hydrogen sulfide (H2S) gas as the sulfur

source. A stock solution of ZnCl2 was prepared and

2032 J Nanopart Res (2009) 11:2031–2041

123

its pH value was adjusted to be in the acidic regime

by the addition of concentrated hydrochloric acid.

This was done to avoid precipitation of zinc hydrox-

ide in solution. For the synthesis of ZnS nanoparticle

chains a p-type silicon (Si) (111) wafer was used as a

substrate to prepare a field emission scanning electron

microscopy (FESEM) sample. The same synthesis

procedure was performed on a 3-mm-diameter car-

bon-coated gold grid as a substrate to obtain a

transmission electron microscopy (TEM) sample. A

volume of 10 lL of a-synuclein fibrils suspended in

the PBS buffer was pipetted onto the, Si wafer,

substrate and dried in a desiccator. The ZnCl2solution (10 lL) was deposited on to the dried

protein solution, followed by an incubation time of

5 min. The substrate with the protein and the ZnCl2solution was then exposed to H2S gas for 5 min.

Later, the substrate was rinsed using deionized water

and dried under a jet of air. A similar procedure was

carried out for the preparation of a TEM sample. A

similar, ZnS nanoparticle chain, TEM sample was

prepared on a carbon-coated gold grid.

Characterization of a-synuclein fibril and ZnS

nanoparticle chains

The diameter and morphology of the a-synuclein

fibril were studied, with TEM, by using the Philips

CM-10 operated under 80 kV accelerating voltage. A

carbon-coated copper TEM grid was used as the

substrate. The protein solution (3 lL) was pipetted

out on to the TEM grid and was stained using 2%

uranyl acetate solution for 1 min. The excess solution

on the grid was then blotted and the sample was used

for imaging.

The average diameter and morphology of the ZnS

nanoparticle chains were analyzed, with FESEM, by

using a Hitachi S4800 field emission scanning

electron microscope and, with TEM, by using an

FEI Titan 80/300 transmission electron microscope.

High-resolution transmission electron microscopy

(HRTEM) images were registered to investigate the

crystalline nature of the sample. Further, an electron

diffraction pattern was obtained to study the crystal

structure of the sample. Electron energy loss spectra

(EELS) were obtained from the ZnS nanoparticle

chains to verify the presence of zinc (Zn) and sulfur

(S) in the samples. Further, elemental mapping of Zn

and S were also obtained to study the distribution of

Zn and S in the samples. Finally, UV–visible (UV–

Vis) absorption spectra were obtained from the ZnS

sample and from the ZnS colloidal sample having a

particle size of 10 lm, purchased from Sigma

Aldrich to compare the absorption peaks. The

FESEM analyses were performed on a Hitachi

S4800. TEM imaging was performed on either

Philips CM-10 operating at 80 kV or on an FEI

Titan 80/300 transmission electron microscope hav-

ing a Gatan Imaging Filter (GIF) and a 2 k CCD,

which operated at 300 kV. EELS and HRTEM

images were registered on the FEI Titan. The UV–

Vis absorption spectra of the ZnS nanoparticle chains

and colloidal ZnS were recorded with a molecular

device microplate reader.

Results and discussion

The a-synuclein fibril formation

The formation of a-synuclein fibrils is believed to

occur through a stepwise mechanism (Conway et al.

2000; Rochet et al. 2000). The incubation of the a-

synuclein protein in PBS, under the conditions

described in ‘Experimental details’, leads to the

formation of small oligomers after a period of

approximately 12 h. These oligomers transform into

protofibrils after an incubation of 36 h in PBS. The

fully formed a-synuclein fibrils are obtained after an

incubation of 96 h. The relationship between the

oligomers, protofibrils, and the fully formed a-synuc-

lein fibrils is still unclear. The TEM image of one such

a-synuclein fibril is shown in Fig. 1a. The twisted

morphology of the fibril can be observed in the image.

Figure 1b is another TEM image of the a-synuclein

fibrils. Here, two fibrils appear to have wound around

each other.

Synthesis and characterization of ZnS

nanoparticle chains

The morphology and average diameter of the nano-

particle chains were obtained after analyzing the

FESEM and TEM images of the ZnS samples.

Figure 2a and b shows one FESEM and one TEM

image, respectively, of ZnS nanoparticle chains. The

average diameter for these samples was approxi-

mately in the range of 60–65 nm. The inset in the

J Nanopart Res (2009) 11:2031–2041 2033

123

TEM image shows the a-synuclein template between

the two ZnS nanoparticles, possibly stained by the

metal salt. The information garnered from the inset

confirms the formation of these nanoparticles on the

a-synuclein template.

High-resolution transmission electron microscopic

imaging was carried out on the ZnS nanoparticle

chains, to study the nanocrystalline nature of the

samples. The HRTEM images indicate that the

nanoparticles are composed of several nanocrystals

which have an approximate dimension of *2 nm.

Figure 3 is a HRTEM image of a ZnS sample. The

lattice fringes are clearly visible, which indicate the

nanocrystalline nature of the ZnS sample, shown in

the inset at the bottom-right of the image. The inset is

a zoomed-in image of a, 2–3 nm sized, ZnS nano-

particle from the highlighted region. It is viewed

along a 110 zone axis and the lattice fringes can be

clearly resolved. The other inset at the top-left of the

image is a Fast Fourier transform (FFT) from the

same highlighted region. This FFT has been indexed

based on the symmetry and lattice spacing and can be

assigned to the FCC pattern along a 110 zone axis,

indicating the zinc blende structure of ZnS.

In addition to the structural information from a

localized area (the single nanoparticle), a selected

area diffraction (SAD) pattern were obtained from

one of the ZnS nanoparticle chains to confirm the

crystal structure. Figure 4 shows a bright field image

of a ZnS nanoparticle chain and the inset shows the

diffraction pattern obtained. The SAD pattern shows

(111), (220), and (311) reflection rings, which match

the spacing of corresponding reflections of ZnS zinc

blende structure, but the (200) reflection is not quite

distinguishable from (111) reflection. However, the

first ring in the SAD pattern has very strong intensity

and broad intensity distribution, and (111) and (200)

lattice spacings of ZnS zinc blende structure from

JCPDS are within the strong and broad first ring. This

is most probably caused by very small sizes (2–3 nm)

of ZnS nanocrystals, as confirmed in Fig. 3. It is very

well known that the diffraction ring from nanocrys-

tals should be much broader compared to its bulk

form. Therefore, based on HRTEM imaging and SAD

Fig. 1 a A single

a-synuclein fibril. b Two

a-synuclein fibrils twisted

around each other

Fig. 2 a FESEM image of

ZnS nanoparticle chains.

b TEM image of ZnS

nanoparticle chains. The

inset is a zoomed-in image

that shows the highlighted

area where what may be a

single a-synuclein fibril can

be clearly seen between two

ZnS nanoparticles

2034 J Nanopart Res (2009) 11:2031–2041

123

pattern, the structure of ZnS nanoparticles in the

chain can be assigned as a zinc blende structure with

little ambiguity.

Along with the SAD results, the presence of Zn and

S in ZnS nanoparticle chains was ascertained by

performing EELS on the ZnS samples. The EELS

obtained from the ZnS sample are shown in Fig. 5a

and b. Figure 5a shows the Zn L3, L2 edges at 1,020

and 1,043 eV. The Zn L1 edge at 1,194 eV is also

clearly visible, even though it is a minor edge.

Figure 5b shows the sulfur L2,3 edge at 165 eV. These

spectra confirm the presence of Zn and S in the sample,

further supporting the SAD results.

Elemental mapping using the Zn L3 edge at

1,020 eV and the S L2,3 edge at 165 eV was also

performed on one of the ZnS nanoparticle chains to

study the distribution of Zn and S in the nanoparticle

chains. Figure 6a shows a zero energy loss image,

followed by the sulfur (Fig. 6b) and zinc (Fig. 6c)

maps. These elemental maps show that Zn and S are

uniformly distributed through the whole nanoparticle

chains.

The next step in the characterization of the ZnS

nanoparticle chains was to perform UV–Vis spectros-

copy on the ZnS nanoparticle chain sample and on ZnS

colloidal sample having a particle size of 10 lm,

purchased from Sigma Aldrich for comparison of the

absorption peaks. To obtain a UV–Vis spectrum, the

sample was prepared in the solution form. The a-

synuclein fibrils, suspended in phosphate buffer, were

pipetted in an Eppendorf tube. To this the ZnCl2solution was added and incubated for 5 min. The H2S

gas was then made to pass through the solution mixture

for 2 min. Another absorption spectrum was obtained

from the colloidal ZnS sample. Figure 7 shows two

UV–Vis spectra obtained from ZnS nanoparticle

chains (a) and ZnS powder (b). The spectrum for

2 min H2S gas exposure showed an absorption peak at

*310 nm. The absorption peak for the colloidal ZnS

sample was obtained at *345 nm. The absorption

peak at *310 nm for the 2 min H2S exposure appears

to have blue shifted (Jovanovic et al. 2007; Yu et al.

2005). This shift is consistent with the quantum

confinement effect. The UV–Vis results were con-

firmed with the help of HRTEM images obtained from

the ZnS nanoparticle chain sample. The HRTEM

images indicate that the nanoparticle chains are

composed of nanocrystals, having a dimension of

*2 nm (20 A´

).

Nanoparticles assembled into functional structures

hold promise for applications in nanocircuitry and

therefore designing nanoparticle chains with con-

trolled electrical properties is of practical and scientific

interest. However, to realize nanoscale interconnects

based on biological templates as building blocks for

nanocircuits, it is critical to achieve control on the

diameter of the synthesized nanostructures. A change

Fig. 3 HRTEM image of ZnS nanoparticle chains. The insetat the bottom-right is a zoomed-in image of the highlighted

region, showing the lattice fringes and the other inset at the

top-left is an indexed FFT from the same highlighted region

Fig. 4 A TEM image of a ZnS nanoparticle chain. The insetshows the SAD pattern obtained from the ZnS sample

J Nanopart Res (2009) 11:2031–2041 2035

123

in the nanoparticle chains’ lateral dimension has a

dramatic influence on the resistance per unit length.

Because of this relationship between size and resis-

tance, the inability to control the nanoparticle diameter

can limit the application of these functional materials

in nanoscale electronic devices. In an attempt to

achieve control of the nanoparticles’ diameters a series

of samples were prepared with varying process

conditions. In the first set of experiments, three

samples were prepared with varying H2S gas exposure

times. The first sample was exposed to H2S gas for

2 min, followed by two more samples exposed for 5

and 10 min, respectively. All the samples were

prepared with a concentration of the salt solution

(ZnCl2) at 2 mM and a pH value of *5.0 for the salt

solution. Figure 8 shows TEM images of ZnS

Fig. 5 Background

subtracted EELS obtained

from ZnS nanoparticle

chains, showing a the Zn

L3, L2, and L1 edges at

1,020, 1,043, and 1,194 eV,

respectively, and b the S

L2,3 edge at 165 eV

Fig. 6 a Zero energy loss image, b sulfur map using L2,3 edge at 165 eV, and c zinc map using L3 edge at 1,020 eV

Fig. 7 UV–Vis spectra obtained from a ZnS nanoparticle

chain sample. a An absorption peak at *310 nm corresponds

to the 2 min H2S gas exposure time. b The next absorption

spectrum was obtained from the colloidal ZnS sample, showing

an absorption spectrum of *345 nm

2036 J Nanopart Res (2009) 11:2031–2041

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nanoparticle chains obtained at varying H2S gas

exposure times. From the TEM images, it can be

clearly seen that the diameter of the ZnS nanoparticles

increases with an increase in the H2S gas exposure

time. The diameter of the nanoparticles thus can be

varied from *30 to *165 nm.

A similar set of experiments was carried out to

investigate the effect of the pH value of the salt

solution (ZnCl2) on the size and morphology of the

ZnS nanoparticle chains. For this experiment three

samples were prepared with varying pH values of the

salt solution. The first sample was prepared with a pH

of 4 followed by the next two samples prepared with

a pH value of 5 and 6. All the samples were

synthesized with a concentration of the salt solution

at 2 mM, and the H2S gas exposure time was 2 min.

Figure 9 shows TEM images of the ZnS nanoparticle

chains obtained by varying the pH values of the salt

solution. From the TEM images, it is evident that the

diameter of the nanoparticles increases with an

increase in the pH value of the salt solution. Thus,

the diameter of the nanoparticle chains can be tuned

by varying the process variables such as H2S gas

exposure time and the pH value of the salt solution.

Controlling the size and packing density of nano-

crystals on a biological scaffold can be an effective

way of tuning the electrical properties of the nano-

structures. To achieve controlled growth kinetics of

nanocrystals on the self-assembled polypeptide scaf-

fold, it is important to understand the parameters that

influence their formation. The reduction of ionic silver

to a metallic form in the presence of proteins and

DNA was first described by Merril et al. (1981) and

Merril (1990). The method is widely applied for the

detection of proteins and nucleic acids and is based on

the differences between the redox potentials of the

biomolecules and those of the matrix. A similar

chemical mechanism, in which the metal ions are

selectively reduced to a metallic form in the presence

of biomolecules was previously used in our laboratory

for the fabrication of inorganic nanoparticle chains on

biological scaffolds, both metallic and semiconduct-

ing (Padalkar et al. 2007, 2008). During the synthesis

process, the cations from a salt source [e.g., AgNO3,

CdCl2, aned Pb(NO3)2] that reacts with the negatively

charged aminoacyl side chains of the protein, at basic

pH (Merril et al. 1981; Merril 1990). When these

cations are subsequently reduced to the elemental

Fig. 8 TEM images of ZnS

nanoparticle chains

obtained after a 2 min,

b 5 min and c 10 min of

H2S gas exposure

J Nanopart Res (2009) 11:2031–2041 2037

123

state, metallic nanoparticle chains grow on the protein

template. The negatively charged C-terminal domain

of a-synuclein contains five aspartate and ten gluta-

mate negatively charged side chains and therefore has

the potential of forming complexes with metal cations

and subsequently nucleating nanocrystals on the fiber

surface. A number of studies have revealed that these

negatively charged side chains into the fibril is not

known with precision, based on our results that show

formation of ZnS nanoparticle chains on the protein

fiber scaffold, it can be speculated that some of these

negatively charged aminoacyl side chains are exposed

at the fiber’s surface rather than buried within the fiber

(Qin et al. 2007; Chen et al. 2007; Heise et al. 2005;

Murray et al. 2003). For semiconductor compounds,

such as ZnS, the metal cations bind to the same

negatively charged aminoacyl side chains of a-

synuclein. After the introduction of the sulfide anion,

semiconductor nanoparticles are expected to nucleate

on the protein fiber surface. It could be speculated that

there are several regions along the protein fiber where

the protein side groups have a significant affinity for

the semiconductor nanoparticles, leading to their

stabilization.

The same generic mechanism could be expanded

to other polypeptide scaffolds and can therefore be of

significant potential importance for the field of

designing bottom–up strategies for nanomaterials

fabrication on biomolecular templates. Our results

prove the biomineralization capacities of the a-

synuclein protein, and can be extended to other

fibrillar proteins or polypeptides.

In an additional experiment, the effect of incuba-

tion temperature of the salt solution on the morpho-

logy of the nanoparticle chains was studied (the

previous studies described in this report were carried

out at 22 �C). Here, two separate experiments were

carried out where the salt solution was heated to a

temperature of 45 and 85 �C for 30 min and then used

in the synthesis process. The pH value of the salt

solution was kept at 5 and the H2S gas exposure time

was fixed to 2 min. Figure 10 shows a TEM image of

a ZnS nanoparticle chain obtained by using a ZnCl2solution at 45 �C. When the ZnS nanoparticle chains

obtained at 45 �C were compared with the ZnS

nanoparticle chains obtained by varying the H2S

exposure time (Fig. 8a) and the pH of the salt solution

(Fig. 9b), it was observed that the ZnS nanoparticles,

Fig. 9 TEM images of ZnS

nanoparticle chains

obtained for different pH

values of the salt solution:

a pH 4, b pH 5, and c pH 6

2038 J Nanopart Res (2009) 11:2031–2041

123

obtained at 45 �C, were very well defined. Figure 10

has several highlighted regions (also shown magnified

in the inset). The left two zoomed-in images show

regions where, may be, the a-synuclein template can

be seen. Although the ZnS nanoparticles look very

well connected, there are a few regions along the

length of the nanoparticle chains that look discon-

nected thus exposing the a-synuclein template. How-

ever, there are many other regions that clearly show

the formation of the neck between the ZnS nanopar-

ticles (shown in the inset to the right).

To improve the connectivity of the ZnS nanopar-

ticles, the ZnCl2 salt solution was heated to a

temperature of 85 �C for 30 min prior to its use in

the synthesis process. The other variables used in the

synthesis process were kept constant, for a better

comparison with the sample obtained at 45 �C.

Figure 11 is a TEM image of a ZnS nanoparticle

chain obtained at 85 �C. When compared with

Fig. 10, it can be clearly seen that the nanoparticles

are well connected and there are no regions where the

a-synuclein template can be seen. The neck regions

that can be seen between ZnS nanoparticles are

shown in the inset for clarity. The neck regions look

very well defined and the ZnS nanoparticle chain

appears more like a nanowire. Thus, by varying the

incubation temperature the connectivity between the

ZnS nanoparticles can be improved.

The changes in the process variables help in

varying the size of the nanoparticle chains and also

help in varying the connectivity between the nano-

particles, thus making the nanoparticle chains more

smoothly connected.

Conclusions

In summary, we report the use of a-synuclein fibrils as

biological templates for the synthesis of ZnS nano-

particle chains. The size of the nanoparticle chains can

be controlled by varying the process variables. This

result was confirmed by TEM imaging carried out on

the ZnS samples. The nanoparticles are composed of

several nanocrystals having a dimension of *2 nm.

The diffraction pattern reveals the zinc blende struc-

ture of ZnS. The EELS confirm the presence of Zn and

S in the ZnS nanoparticle chains. Further, elemental

mapping of Zn and S shows uniform distribution of

both the elements on the nanoparticle chains.

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